Now that I have had a chance to run it at our local Trainshow this week, my FlyerChief Berkshire is definitely my favorite AF loco (even though I'm still miffed about the cast on boiler handrails which are clearly stated in the catalog to be separately applied). The FlyerChief control system is terrific! My favorite O-3 rail loco is my LionChief Plus PRR Mikado, for similar reasons. I also have a LionChief O gauge Thomas that I'm pretty fond of, but I do wish it was a LionChief Plus loco.
In second place for AF favorites are their EP5's, especially after a club member brought his Milwaukee unit to run on the small loop at our local Trainshow this week.
Bill in FtL